Integrated connector module with conductive elastomeric contacts

ABSTRACT

An electrical conductor that electrically couples a circuit board to another electrical device. The connector has a flexible circuit board with at least one electrical conductor that is attached to a flexible dielectric sheet. Attached to the electrical conductor is an electrically conductive elastomer adapted to engage conductive pads on the surface of the circuit board. The connector has a plate or other member that presses the conductive elastomer onto the conductive surface pads, creating an electrical path between the conductor and the circuit board. The conductor is attached to the electrical device, wherein the electrical device is electrically coupled to the circuit board.

This is a divisional of application Ser. No. 667,420, filed Mar. 11,1991, now U.S. Pat. No. 5,123,851.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to electrical connectors used toelectrically couple two electronic boards or devices together.

2. Description of Related Art

Computers or other similar type electronic systems will typically havediscrete electrical devices soldered to printed circuit boards (PCB's).The devices are usually packaged in plastic carriers that have copperleads which extend through the printed circuit boards, to provide anelectrical connection between the device and the PCB. Routing space forthe conductors within the PCB is reduced because the lines must goaround the leads extending through the board. To increase routingdensity, methods have been devised to mount the devices onto the surfaceof the PCB's, without the extended leads and accompanying plated throughholes in the boards. One common method of surface mounting components,is to provide electrically conductive pads on the surface of the PCB andwave soldering the components to the pads. Because there are no leadsextending through the board it is now possible to mount components onboth sides of the board, greatly increasing the electronic density ofthe board.

An assembled PCB will typically communicate with other electricaldevices such as a computer keyboard, a printer, or another board. Thisis usually done with a pair of mating connectors, wherein the connectorshave electrically conductive leads that are soldered to the PCB. Theleads are wave soldered to the boards in the same manner as thecomponents. Usually the connector is attached to the PCB after thecomponents have already been soldered to the board. To solder theconnector, the whole board must be raised to the solder melting point.When a connector is soldered to a board with components on both sides,the components of the board facing down fall off the board.Additionally, every time the board is subjected to wave soldering thePCB is degraded, especially the surface pads. It is therefore desirableto have an electrical connector that can interconnect a PCB and anotherelectrical device without soldering the conductors to the PCB. Repairingthe connector is also difficult, wherein the board must again bereflowed. This requires moving the board to a wave solder machine, whichis large, expensive and usually only found in manufacturing facilities.It would be preferable to remove the connectors "on site", without theneed for a soldering device.

The ever increasing capacity of integrated circuits and routing of thePCB's has greatly increased the input/output (I/O) requirements of theconnectors. Standard connectors are typically constructed with 0.100inch centers, with some "high density" connectors having 0.050 inchcenters. It has been found that such connectors are insufficient tohandle the I/O requirements of some of the present computer systemsbeing designed. It would therefore be desirable to have a connector thathas spacing lower than 0.050 inches.

SUMMARY OF THE INVENTION

The present invention is an electrical connector that electricallycouples a circuit board to another electrical device. The connector hasat least one electrical conductor that is attached to a flexibledielectric sheet to form a flexible circuit board commonly known as a"flex-circuit". Attached to the electrical conductors is an electricallyconductive elastomer adapted to engage conductive pads on the surface ofthe circuit board. The connector has a plate or other member thatpresses the conductive elastomer onto the conductive pads, creating anelectrical path between the conductors and the circuit board. Theconductor is attached to the electrical device, wherein the electricaldevice is electrically coupled to the circuit board.

The elastomer is typically made from silicon rubber that has apredetermined amount of electrically conductive material. When therubber is compressed, the density of the conductive filler increasessuch that the rubber becomes an electrical conductor. The plate can bescrewed onto the circuit board to apply pressure to the conductiveelastomer to couple the board and the device. The circuit board can thenbe disconnected by merely unscrewing the screws and removing the board.The other electrical device can be another circuit board or a standardpin or card edge connector.

The use of a flex circuit allows the conductors to be spaced on 0.010inch centers, which greatly increases the I/O capability of theconnector and the routing density of the PCB.

Therefore it is an object of this invention to provide an electricalconnector that has an electrical interface that is not soldered to acircuit board.

It is also an object of this invention to provide an electricalconnector that provides a spacing density of 0.010 inches.

It is also an object of this invention to provide an electricalconnector that has a low profile.

It is also an object of this invention to provide an electricalconnector that allows the connector to be removed from an circuit boardwithout using a soldering device or heating any portion of the boardthereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the present invention will become morereadily apparent to those skilled in the art after reviewing thefollowing detailed description and the accompanying drawings, wherein:

FIG. 1 is a diagrammatical side view of an electrical connector of thepresent invention;

FIG. 2 is a perspective view of an electrical connector showing aconductive elastomer attached to a conductor, such that the elastomercan be pressed onto a surface pad by a plate screwed into a circuitboard;

FIG. 2a is a perspective view showing a portion of a plate that isattached to a circuit board by a clip;

FIG. 3 is a side view of an electrical connector showing conductiveelastomeric strips attached to individual conductors of a flexiblecircuit board;

FIG. 4 is a side view similar to FIG. 3 showing the conductiveelastomeric strips pressed onto surface pads of a circuit board;

FIG. 5a is a top view of a flexible circuit board with a plurality ofconductive elastomeric strips attached to conductors exposed by a windowcut into the dielectric sheet of the flexible circuit board;

FIG. 5b is a bottom view of a retaining block that holds an elastomericblock comprising adjacent layers of conductive and nonconductiveelastomeric strips;

FIG. 5c is a side view of a retaining block attached to a plate byscrews that thread into a circuit board and compress the elastomericblock with the retaining block;

FIG. 6 is a top view of a flexible circuit board similar to FIG. 5a,showing an environmental rubber seal attached to the flexible circuit;

FIG. 7 is a side view of two surface mounted circuit boards electricallycoupled by electrical connectors of the present invention;

FIG. 8 is a perspective view of a portion of a circuit board showingboth sides of the board electrically coupled by an electrical connectorof the present invention;

FIG. 9 is a perspective view of a connector module that has a block thathouses a pin connector which is attached to a plurality of connectors ofthe present invention, the block has a pair of screws to attach theblock to a circuit board and to apply pressure to elastomeric stripsunder the flexible circuit boards.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings more particularly by reference numbers, FIG. 1shows a basic embodiment of an electrical connector 10 of the presentinvention. The connector 10 electrically couples a circuit board 12 toanother electrical device 14. The circuit board 12 will typically havesurface mounted components attached to both sides of the board 12, withelectrically conductive pads 16 on the surface 18 thereof. The pads 16are attached to conductive lines that ultimately connect with thecomponents. The pads 16 are preferably etched from copper and thenplated with gold. The other device 14 can be another circuit board withthe same assembly of components and pads as described above.

The connector 10 has at least one electrical conductor 20, preferablyconstructed from copper, that is attached at one end to the electricaldevice 14. On each side of the conductor 20 are sheets of flexibledielectric material 22 that is sold by E.I. DuPont de Nemours & Co.under the trademark KAPTON. The flexible dielectric 22 and conductor 20form a flexible circuit board 24 commonly known in the art as aflex-circuit. Attached to the other end of the conductor 20 is anelectrically conductive elastomer 26. Opposite the elastomer 26 is aplate 28 that applies a pressure to the conductor 20 and elastomer 26,pressing the elastomer 26 onto the surface pad 16 of the circuit board12. The elastomer 26 is preferable constructed from rubber that has apredetermined amount of electrically conductive material, such that whenthe elastomer 22 is compressed it becomes electrically conductive. Theelectrically conductive material can be metal particles, minute wires,carbon fibers or small springs that are interposed throughout therubber. Without being limited by the theory thereof, it is believed thatwhen the rubber is compressed, the density of the conductive materialincreases such that the fibers, etc. come into contact with each otherto create an electrical path through the elastomer. A spring filledelastomer is preferred in that it has been found that this particulartype of elastomeric conductor has the lowest electrical resistance,typically on the order of 0.1 ohms/cm. Silicon rubber is preferred,because silicon is resistive to many types of chemicals and siliconrubbers do not permanently set when compressed by pressures typicallyseen in this application.

As shown in FIG. 2, the elastomer 26 can be compressed by attaching theplate 28 to the circuit board 12, with a pair of screws 30 that screwinto a pair of threaded apertures 32 in the board 12. The pressure ofthe plate 28 can be adjusted by turning the screws 30 and moving theplate 28 relative to the circuit board 12. Although screws 30 are shownit is understood that other means of applying pressure to the elastomer22 can be employed. For example, metal clips 34 can be incorporated thatrotate and fasten the plate 28 to the board 12 as shown in FIG. 2a.These types of fasteners are known in the art and provide a quick way ofattaching and detaching the connector 10. FIGS. 3 and 4 show a morepreferred embodiment of the conductor 20, wherein the copper isconstructed into a plurality of conductive leads 36. Each conductivelead is coupled to a corresponding conductive pad 16. The individualleads 36 would be ideally used to transmit digital signals. Attached toeach conductor 36 is a conductive elastomeric strip 38 that engages thesurface pads 16 of the circuit board 12. The elastomer 38 is of suchthickness and having a modulus of rigidity, such that a minimal force isneeded to compress the rubber sufficiently to create an electrical pathbetween the surface pads 16 and the conductors 36. For example it hasbeen found that for conductor leads 0.005 inches wide, the elastomericstrips 38 should be approximately 0.125 inches thick. The 0.005" wideconductors 38 allow the connector 10 and surface pads 16 to beconstructed with 0.010 inch centers. As shown in FIG. 4, the elastomericstrips 36 will increase in width or bulge when compressed. The spacingbetween conductors 36 and strips 38 should be such that there is asufficient gap between the strips 38 to prevent shorting of adjacentconductors 36. The dielectric 22 provides electrical insulation betweenthe conductors 38 and the plate 28, so that the plate 28 can beconstructed from metal. It is preferable to have a stiff plate so thatthe forces applied at the ends as shown in FIGS. 2 and 2a, translateacross the plate, to insure that the pressure on each strip across thelength of the plate is approximately the same. FIG. 5a shows a patternof conductors 36 in a flex-circuit 24. The conductors 36 areencapsulated by two sheets of KAPTON, wherein a window 40 is cut intoone sheet of the KAPTON to expose a portion of the conductors 32. Theelastomeric strips 38 are then attached to the exposed conductors 32 bybonding a portion 44 of the strips 38 to the KAPTON 22 outside thewindow 40. FIGS. 5b and 5c show a preferred embodiment that has anelastomeric block 42 attached to the window 40 of the flex-circuit 24.The elastomeric block 42 comprises a plurality of conductive elastomericstrips 38 adjacent and attached to a plurality of nonconductiveelastomeric strips 44. Such an elastomeric block 42 is sold by Fujipoly,Inc. under the trademark ZEBRA. The nonconductive strips 44 providestructural support and electrical insulation for the conductive strips38. The elastomeric block 42 can be held in place by a retaining block46 with a cavity 48 of such dimension to hold the elastomers. Thehousing 46 can be attached to the plate 28 by screws 30 that extendthrough the plate 28 and housing 46 as shown in FIG. 5c. The screws 30thread into the circuit board 12 pressing the elastomeric block 42against the conductive pads 16. To provide environmental protection, anannular ring 50 of nonconductive rubber can be attached to theflex-circuit 24 outside the window 40, as shown in FIG. 6. The ring 50could be formed with the individual elastomeric strips 38 or with anelastomeric block 42 for ease of assembly. The annular ring 50 is alsocompressed by the plate 28, such that the strips 38 are sealed from theenvironment. The pressure of the seal 50 should be such to prevent fluidor gaseous communication between the elastomeric strips 38 and the areaoutside the seal 50. With this embodiment, condensation or other foreignmatter can not enter the region of the strips 38 and electrically shortcircuit the conductors 36.

FIGS. 7 and 8 show alternate uses of the connector of the presentinvention. FIG. 7 shows the interconnection of two circuit boards 12,both having surface mounted components. The boards 12 are electricallycoupled by flex-circuits 24 similar to that shown in FIG. 5a, whereinelastomeric strips 38 are attached to exposed conductors 36 on both endsof the circuit 24. The strips 38 engage conductive pads 16 that areetched into the surface of the boards 12. Plates 28' can be interposedbetween the ends of the circuit 24. The boards 12 are pressed togethercompressing the strips 38 onto the pads 16 of each board 12. Thisarrangement allows for easy disconnection of the boards 12, withoutheating the boards as was done in the prior art. The present connector10 also provides a lower profile than present pin connectors that aretypically used today. The spacing between the boards 12 now only beinglimited by the height of the components mounted on the boards 12. Thisgreatly increases the overall density of the electronic assembly. FIG. 8shows another use of the connector wherein the flex-circuit 24electrically couples both sides of a board 12. This is particularlyuseful when components are mounted on both sides of a board 12 and eachside must communicate with one another. The elastomeric strips 38 can becompressed by two plates 24 bolted together by a pair of screws 30. Theconnector of FIG. 8 could be modified such that the flex-circuit hasplated through holes in the center adapted to attach to the leads of astandard pin connector. Such a connector interface would allow astandard pin connector to be removed from a board, without locallyheating the board to remove the soldered leads of the connector from theboard.

FIG. 9 shows, another embodiment of the present invention. Flex circuits24 constructed as shown in FIG. 5a, are attached to the bottom of plates52 that induce contact between elastomeric strips and surface pads onthe circuit board 12. The plates 52 have flanges 54 that are insertedinto slots 56 in the board that align the conductive elastomeric stripswith the conductive pads. The other end of the flex-circuits 24, aresoldered to connectors 58 that are housed in a connector block 60. Theconnectors 58 typically being standard pin or card edge electricalconnectors. Attached to the block 60 is a plate 62 with a pair offlanges 64 and screws 66 that bolt the block 60 to the circuit board 12.As an alternative to the plate 62, the block 60 could be constructed tohave flanges. The bottom of the block 68 engages both ends of the plates52 and applies pressure to the elastomeric strips when the block 60 andboard 12 are attached. The block 60 can have four channels 70 thatdefine two trays that allow mating connectors to be plugged into theconnectors 58 housed in the block 60. Typically each tray will have asingle connector, wherein the channels 70 guide the mating connectorstogether. The channels 70 could also have keying features to prevent thewrong connector from making contact with the connector in block 60. Thuswhat is disclosed is a connector module that can be readily detachedfrom a circuit board without having to heat the board as is presentlydone in the art. This greatly increases the repairability and life ofthe board, allowing a circuit board to be easily removed from a computerby merely unscrewing two screws 66. The module of this embodiment ispreferably used to connect an I/O card to external devices such as aprinter.

While certain exemplary embodiments have been described in detail andshown in the accompanying drawings, it is to be understood that suchembodiments are merely illustrative of, and not restrictive on the boardinvention, and that this invention not be limited to the specificconstructions and arrangements shown and described since various othermodifications may occur to those ordinarily skilled in the art.

What is claimed is:
 1. An electronic card, comprising;a printed circuitboard having a plurality of conductive pads; an electrical connectormounted onto said printed circuit board; a flexible circuit board havinga plurality of conductors attached to a flexible dielectric sheet, saidconductors having a first end and a second end attached to saidelectrical connector; a plurality of conductive elastomeric stripsattached to and carried by said first ends of said conductors and beingconstructed to provide an electrical path between said conductors andsaid conductive pads when pressure is applied to said conductiveelastomeric strips, each elastomeric strip being separated by a space;and, pressure means for applying an operative pressure to saidconductive elastomeric strips.
 2. The electronic card as recited inclaim 1, further comprising a seal that is attached to said conductiveelastomeric strips and encloses said conductive elastomeric strips.
 3. Amethod of removing a connector from a printed circuit board, comprisingthe steps of;providing;a printed circuit board having ak plurality ofconductive pads; an electrical connector mounted onto said printedcircuit board; a flexible circuit board having a plurality of conductorsattached to a flexible dielectric sheet, said conductors having a firstend and a second end attached to said electrical connector; a pluralityof conductive elastomeric strips attached to and carried by said firstends of said conductors and being constructed to provide an electricalpath between said conductors and said conductive pads when pressure isapplied to said conductive elastomeric strips, each elastomeric stripbeing separated by a space; pressure means for applying an operativepressure to said conductive elastomeric strips; disengaging saidpressure means; removing said conductive elastomeric strips from saidconductive pads; removing said electrical connector from said printedcircuit board.